This invention relates to a composition which is settable by the reaction of a silicate with a hardener, more particularly to a composition provided in two parts to be mixed, each part formulated to have improved storage stability. When the parts are mixed the composition is useful for a variety of purposes for example anchoring anchor elements in the roof of a mine to secure the roof strata to overlying rock formations.
It has been previously proposed to provide hardenable silicate compositions in two part form and this is described in U.S. Pat. No. 5,165,958 which describes a method of sealing mine stoppings where an alkali metal silicate solution provided in one part is gelled by reaction with a weak acid or acid salt or ester that hydrolyses to release acid provided in another part. U.S. Pat. No. 5,330,785 describes the use of a similar two part composition to seal rock strata.
It is a problem with two part settable silicate compositions that they have only a limited shelf life, especially when they are stored under very hot or humid conditions which are sometimes found in mines.
A solution to this problem has now been invented in which the two parts of the settable silicate composition have an improved shelf life.
According to one aspect of the present invention there is provided a substantially water-free hardener composition suitable for admixture with a cement to give a product capable of reaction with a silicate to form a hardened mass, said hardener composition comprising:
(a) from 50 to 99.9% of an organic carbonate hardener for the silicate
(b) from 0.01 to 20% of an organic retarder preferably an organic acid retarder for the cement, the % being by weight based on the total weight of (a) and (b).
Preferably the amount of carbonate is from 75 to 99.8% and the amount of organic acid retarder is from 0.02 to 10%.
The carbonate may conveniently be ethylene carbonate, propylene carbonate, or butylene carbonate and is preferably a dry blend of ethylene carbonate (which is a solid at room temperature) in liquid propylene carbonate.
Preferably the organic carbonate hardener is a mixture of ethylene and propylene carbonates in proportions of from 3:1 to 1:3 by weight.
The hardener composition preferably includes a cement.
Therefore according to a preferred embodiment of the invention a hardener composition for reaction with a silicate to form a hardened mass, comprises:
a) from 10 to 60% of an organic carbonate hardener for the silicate
b) from 0.05 to 5% of an organic retarder preferably an organic acid retarder for the cement and
(c) from 20 to 85% of a cement capable of reacting with the silicate, the % being by weight based on the total weight of (a), (b) and (c).
By adjusting the amounts of (a), (b) and (c) it is possible to form the composition as a stable paste ie where the solids do not settle out and also to achieve a storage life of at least 12 weeks at 35 degrees Centigrade.
Preferably the blend of carbonates makes up about 20% to about 40%, most preferably about 25-35% by weight of the water free hardener composition.
In addition to the carbonate other organic hardeners for silicates may be employed, e.g. AGS esters, triacetin, diacetin; and the like.
It has been found experimentally that ethylene carbonate, propylene carbonate and buylene carbonates result in different gel times. In the case of ethylene carbonate alone the gel time is about 15 seconds whereas with buylene carbonate it is about 20 minutes. By emptying a mixture and adjusting the proportions of these carbonates it is possible to adjust the gel time between about 5 seconds and 20 minutes.
It was initially expected that a dry mixture of organic carbonate and cementitious material would be stable but it was found by experiment to harden after about 3 weeks at 35xc2x0 C. However it was then found unexpectedly that the addition of an organic acid known as a retarder for the reaction of cements with water, produced a stable composition that was usable after storage for 12 weeks at 35xc2x0 C.
The cement is preferably Ordinary Portland Cement (OPC) which makes up the major constituent. Other cements may also be present in addition to, or in substitution for the OPC, e.g. calcium sulphoaluminate (CSA, high alumina cement (HAC), plaster, ground granulated blast furnace slag (GGBFS), pulverised fuel ash (PFA) and the like.
The hardener composition may include other ingredients, for example, suspension agents such as bentonite, say up to 10%; retarders; extenders; accelerators; dispersants; and the like.
According to another aspect of the invention there is provided a silicate-containing composition for reaction with the hardener composition to form a hardened mass, said silicate composition comprising:
a) from 50 to 85%, preferably 50 to 80% of a filler,
(b) from 3 to 40%, preferably 5 to 25% of an alkali metal silicate
(c) from 5 to 70%, preferably 10 to 50% water
the percentages being by weight based on the total weight of (a), (b) and(c) and the amount of alkali metal silicate being on a dry basis.
By adjusting the amounts of (a), (b) and (c) it is possible to produce the composition in the form of a stable paste ie where the solids do not settle out and also to achieve a storage life of at least 12 weeks at 35 degrees centigrade.
The composition may include other inorganic settable substance; fillers; and the like. Preferably the composition includes an orthophosphate to act as retarder and/or dispersant; accelerators; extenders; and the like.
The silicate may be an alkali metal silicate for example sodium or potassium silicate and may have a silica to alkali metal oxide molar ratio of from 2: to 4:1. Alkali metal silicates are usually associated with water and the silicate may have a solids content of from 10 to 60% by weight, typically about 30 to 50%, the balance being water.
References to the amount of alkali metal silicate in the silicate base composition are calculated on a water-free basis.
The silicate-containing composition may contain a filler provided it is non reactive and compatible with the silicate for long term stability. Such fillers include limestone, mica, cellulose fibre, glass fibre, and other reinforcing non reactive fibres, clay and kaolin.
It is an object of the invention to prolong the shelf life of the silicate base composition as well as that of the hardener composition. Generally the lower the molar ratiof silica to sodium oxide the shorter is the shelf life. When the molar ratio is raised to about about 3.3:1 the shelf life is extended but the gel time is too short. However it has been discovered that if the molar ratio of silica to alkali metal oxide in a silicate is lowered from for example 3.3:1 to about 2.8:1 by the addition of sodium hydroxide or the like the gel time is extended without loss of shelf life.
For example, adding sufficient sodium hydroxide to sodium silicate having a molar ratio of silica: sodium oxide of 3.3:1 to give a molar ratio of 2.8:1 gives a shelf life greater than 12 weeks at 35xc2x0 C.
According to one embodiment of the invention there is provided a compartmented container having two compartments impervious to air and water, one compartment containing a hardener composition as hereinbefore defined and the other compartment containing a silicate-containing composition as hereinbefore defined.
The relative amounts of amounts of reactive components are preferably chosen so that when the compositions in the two compartments are mixed the reactants will form a hardened mass.
Conveniently the relative amounts of ethylene carbonate, propylene carbonate and butylene carbonate are adjusted to give a gel time of within 15 seconds and 20 minutes.
The invention includes a method of reacting the two part composition for purposes other than anchoring an anchor element.
The cement may contain traces of moisture such as are found in commercially available forms of these materials and references to dry and substantially water-free should be construed accordingly.
In order that the invention may be well understood it will now be described, by way of illustration only, with references to the following examples in which parts are by weight and strengths are in MPa.